Method and Apparatus for Transmitting and Receiving Client Signal

ABSTRACT

Embodiments of the present invention provide a method and an apparatus for transmitting and receiving a client signal, and relate to the field of communications technologies. The method includes: mapping the client signal into channels of a parallel transmission frame, where the parallel transmission frame includes at least two channels; adding an overhead for the channels of the parallel transmission frame after the mapping, to form transmission channels of the parallel transmission frame, where bit rates of the transmission channels of the parallel transmission frame are fixed; and modulating the transmission channels of the parallel transmission frame onto one or more optical carriers in a same optical fiber, and transmitting the optical carrier after the modulation.

This application is a continuation of International Application No.PCT/CN2012/076916, filed on Jun. 14, 2012, which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

The present invention relates to the field of communicationstechnologies, and in particular, to a method and an apparatus fortransmitting and receiving a client signal.

BACKGROUND

An OTN (optical transport network), as a core technology of anext-generation transport network, includes electrical layer and opticallayer technical specifications, has rich OAM (operation, administrationand maintenance) functions, a strong TCM (tandem connection monitoring)capability, and an outband FEC (forward error correction) capability,and can implement flexible scheduling and management of a large-capacityservice.

An existing OTN system has four fixed line rates OTUk (optical channeltransport unit, where k=1, 2, 3, 4 which correspond to rate levels of2.5G, 10G, 40G, 100G respectively), and a service can be adapted intoonly the four fixed line rates OTUk. For example, at a site A, a 40GEfour-channel parallel signal needs to be aggregated with a 10GE signal,and transmitted to a site B. In this case, an OTU4/ODU4 may be selectedto perform aggregation. The 40GE four-channel parallel signal is firstconverted into a serial 64B/66B code stream, and is mapped to an LO ODU3after being processed, and then is mapped to 31 timeslots of an HO ODU4;for the 10GE signal, the 10GE signal is first mapped to an ODU2e, andthen is mapped to 8 timeslots of the HO ODU4; after a supervisoryoverhead is added to the HO ODU4, an OTU4 frame is formed. Generally,the OTU4 uses a low-cost OTL4.n (n=4, 10) multichannel parallelinterface, and therefore the OTU4 needs to be further distributed toform the OTL4.n interface, and then the OTL4.n is modulated onto anoptical carrier for transmission.

However, on one hand, with a great increase in upper-layer IP services,currently a beyond 100G technology, for example, a 400G or 1T opticaltransport technology with higher spectral efficiency, is researched inthe industry. In order to achieve an optimized and most efficientnetwork configuration to improve efficiency of using optical spectrumresources, a Flex Grid technology is introduced to the optical layer toexpand the spectrum from a conventional fixed 50 GHz spectral grid(ITU-T G.694) to a flexible spectral grid with a smaller granularity,where slot=12.5 GHz (a central frequency is 193.1 THz+n×slot/2, andspectral bandwidth is m×slot). In this way, a signal may occupy multipleconsecutive spectral grids.

Changing a modulation format, a carrier symbol rate, and the number ofmultiple subcarriers implements that spectral bandwidth changesflexibly, thereby improving effective utilization of the spectrumresources and improving bandwidth usage. On the other hand, in terms ofclient services, with a rapid growth of data services, an increasingamount of information is encapsulated by using an Ethernet, FC (fiberchannel), and ESCON (enterprise system connection) technology, and thenumber of rate levels is increasing. In order to flexibly support thedata services, the OTN is additionally provided with ODUflex (opticalchannel data unit flex) to adapt data services with various bandwidthrequirements. However, the line rates of the OTN still use fixedbandwidths of 2.5G, 10G, 40G, and 100G, which is not beneficial to moreefficient use of transmission bandwidth. In addition, an increasingnumber of client signals use a multi-wavelength parallel interface, forexample, a 100GE multichannel parallel interface, to replace theconventional serial interface, so as to implement low-cost access of ahigh-speed service. At the present, in order to adapt a client signal ofa multi-wavelength parallel interface into an OTN parallel interface, amanner of “multiplexing, distribution, and multiplexing” is still used,and therefore processing is quite complex.

As described above, in a process in which a client signal and opticallayer spectral bandwidth evolve to higher-rate ones, both the clientsignal and the optical layer technology have a trend of flexibilizationand parallelization. Therefore, it is a to-be-resolved problem that howthe transport network evolves to further simplify a service processingprocess, thereby improving bandwidth usage and reducing networkcomplexity, so as to adapt to a variation trend of the client signal andthe optical layer spectral bandwidth.

SUMMARY

To enable a transport network to adapt to a change in a client signaland optical layer spectral bandwidth, embodiments of the presentinvention provide a method and an apparatus for transmitting andreceiving a client signal. The technical solutions are as follows:

According to one aspect, a method for transmitting a client signal isprovided, where the method includes: mapping the client signal intochannels of a parallel transmission frame, where the paralleltransmission frame includes at least two channels; adding an overheadfor the channels of the parallel transmission frame after the mapping,to form transmission channels of the parallel transmission frame, wherea management overhead is added to one of the channels of the paralleltransmission frame after the mapping, the management overhead is used tocentrally manage the channels of the parallel transmission frame afterthe mapping, and bit rates of the transmission channels of the paralleltransmission frame are fixed; and modulating the transmission channelsof the parallel transmission frame onto one or more optical carriers ina same optical fiber, and transmitting the optical carrier after themodulation.

A rate of the parallel transmission frame depends on the number oftransmission channels of the parallel transmission frame and the bitrates of the transmission channels.

When the bit rates of the transmission channels of the paralleltransmission frame are equal, the number of transmission channels of theparallel transmission frame is adjusted to form a parallel transmissionframe with a changeable rate.

The mapping the client signal into channels of a parallel transmissionframe includes: when a rate of the client signal is greater than atransmission rate of a single channel of the parallel transmissionframe, splitting the client signal to obtain multiple client signalsafter the splitting, and mapping the multiple client signals that areobtained after the splitting into corresponding channels of the paralleltransmission frame; or when a rate of the client signal is less than atransmission rate of a single channel of the parallel transmissionframe, mapping the client signal into one channel of the paralleltransmission frame; or when the client signal is a multichannel parallelclient signal and a rate of a single channel of the multichannelparallel client signal is less than a rate of a single channel of theparallel transmission frame, mapping each channel of the multichannelparallel client signal into a corresponding channel of the paralleltransmission frame.

The overhead added for the channels of the parallel transmission frameafter the mapping includes: a frame header identifier and a mappingoverhead, where the frame header identifier is used to identify a startof a channel of the parallel transmission frame, and the mappingoverhead is used to indicate a location, into which the client signal ismapped, in the channel.

The overhead added for the channels of the parallel transmission frameafter the mapping further includes: one or more of a channel numberidentifier and a forward error correction FEC code, where the channelnumber identifier is used to distinguish each channel of the paralleltransmission frame after the mapping, and the FEC code is used toprovide the channels of the parallel transmission frame with a forwarderror correction function.

The management overhead includes: information about allocation of acorresponding channel of the parallel transmission frame to acorresponding client signal and/or information indicating a type of aclient signal carried by a corresponding channel of the paralleltransmission frame.

The management overhead further includes: a lane monitor overhead and/oran automatic protection switching overhead, where the lane monitoroverhead is used to monitor the channels of the parallel transmissionframe, and the automatic protection switching overhead is used toimplement automatic switching of the channels of the paralleltransmission frame in case of a fault, so as to recover transmission ofthe client signal.

The modulating the transmission channels of the parallel transmissionframe onto one or more optical carriers in a same optical fiberincludes: separately modulating each channel in the transmissionchannels of the parallel transmission frame onto an optical subcarrierin a corresponding number of multiple optical subcarriers in the sameoptical fiber; or dividing the transmission channels of the paralleltransmission frame into N groups of transmission channels, where eachgroup includes M transmission channels, and M is the number ofsubcarrier modulation phases, modulating each group of M transmissionchannels onto one optical subcarrier, and separately modulating the Ngroups of transmission channels onto N optical subcarriers in the sameoptical fiber; or multiplexing the transmission channels of the paralleltransmission frame into one data stream or data streams whose number isless than the number of transmission channels, and modulating the onedata stream or the data streams whose number is less than the number oftransmission channels onto a single optical carrier or a correspondingnumber of optical carriers in the same optical fiber; or splitting eachtransmission channel of the parallel transmission frame into multipledata streams with a preset rate, and separately modulating the multipledata streams corresponding to each split transmission channel ontomultiple subcarriers in the same optical fiber.

According to another aspect, a method for receiving a client signal isprovided, where the method includes: receiving one or more opticalcarriers in a same optical fiber, and demodulating transmission channelsof a parallel transmission frame from the optical carrier; parsing anoverhead of the transmission channels of the parallel transmissionframe, to obtain channels of the parallel transmission frame, where theoverhead includes a frame header identifier, a mapping overhead, and amanagement overhead that is extracted from one transmission channel inthe transmission channels of the parallel transmission frame, where themanagement overhead is used to centrally manage the channels of theparallel transmission frame, and bit rates of the transmission channelsof the parallel transmission frame are fixed; and demapping the clientsignal from the channels of the parallel transmission frame according tothe frame header identifier, the mapping overhead, and the managementoverhead.

According to another aspect, an apparatus for transmitting a clientsignal is further provided, where the apparatus includes: a mappingmodule, configured to map the client signal into transmission channelsof a parallel transmission frame, where the parallel transmission frameincludes at least two channels; an overhead adding module, configured toadd an overhead for the channels of the parallel transmission frameafter the mapping module performs the mapping, to form transmissionchannels of the parallel transmission frame, where a management overheadis added to one of the channels of the parallel transmission frame afterthe mapping, the management overhead is used to centrally manage thechannels of the parallel transmission frame after the mapping, and bitrates of the transmission channels of the parallel transmission frameare fixed; and a modulation and transmission module, configured tomodulate the transmission channels of the parallel transmission framethat are formed by the overhead adding module onto one or more opticalcarriers in a same optical fiber, and transmit the optical carrier afterthe modulation.

A rate of the parallel transmission frame depends on the number oftransmission channels of the parallel transmission frame and the bitrates of the transmission channels.

The apparatus further includes: a channel adjustment module, configuredto: when the bit rates of the transmission channels of the paralleltransmission frame are equal, adjust the number of transmission channelsof the parallel transmission frame to form a parallel transmission framewith a changeable rate.

The mapping module includes: a first mapping unit, configured to: when arate of the client signal is greater than a transmission rate of asingle channel of the parallel transmission frame, split the clientsignal to obtain multiple client signals after the splitting, and mapthe multiple client signals that are obtained after the splitting intocorresponding channels of the parallel transmission frame; or a secondmapping unit, configured to: when a rate of the client signal is lessthan a transmission rate of a single channel of the paralleltransmission frame, map the client signal into one channel of theparallel transmission frame, to obtain the parallel transmission frameafter the mapping; or a third mapping unit, configured to: when theclient signal is a multichannel parallel client signal and a rate of asingle channel of the multichannel parallel client signal is less than arate of a single channel of the parallel transmission frame, map eachchannel of the multichannel parallel client signal into a correspondingchannel of the parallel transmission frame.

The overhead added for the channels of the parallel transmission frameafter the mapping includes: a frame header identifier overhead and amapping overhead, where the frame header identifier is used to identifya start of a channel of the parallel transmission frame, and the mappingoverhead is used to indicate a location, into which the client signal ismapped, in the channel.

The overhead added for the channels of the parallel transmission frameafter the mapping further includes: one or more of a channel numberidentifier and a forward error correction FEC code, where the channelnumber identifier is used to distinguish each channel of the paralleltransmission frame after the mapping, and the FEC code is used toprovide the channels of the parallel transmission frame with a forwarderror correction function.

The management overhead includes: information about allocation of acorresponding channel of the parallel transmission frame to acorresponding client signal and/or information indicating a type of aclient signal carried by a corresponding channel of the paralleltransmission frame.

The management overhead further includes: a lane monitor overhead and/oran automatic protection switching overhead, where the lane monitoroverhead is used to monitor the channels of the parallel transmissionframe, and the automatic protection switching overhead is used toimplement automatic switching of the channels of the paralleltransmission frame in case of a fault, so as to recover transmission ofthe client signal.

The modulation and transmission module includes: a first modulationunit, configured to separately modulate each channel in the transmissionchannels of the parallel transmission frame onto an optical subcarrierin a corresponding number of multiple optical subcarriers in the sameoptical fiber; or a second modulation unit, configured to divide thetransmission channels of the parallel transmission frame into N groupsof transmission channels, where each group includes M transmissionchannels, and M is the number of subcarrier modulation phases, modulateeach group of M transmission channels onto one optical subcarrier, andseparately modulate the N groups of transmission channels onto N opticalsubcarriers in the same optical fiber; or a third modulation unit,configured to multiplex the transmission channels of the paralleltransmission frame into one data stream or data streams whose number isless than the number of transmission channels, and modulate the one datastream or the data streams whose number is less than the number oftransmission channels onto a single optical carrier or a correspondingnumber of optical carriers in the same optical fiber; or a fourthmodulation unit, configured to split each transmission channel of theparallel transmission frame into multiple data streams with a presetrate, and separately modulate the multiple data streams corresponding toeach split transmission channel onto multiple subcarriers in the sameoptical fiber.

According to another aspect, an apparatus for receiving a client signalis further provided, where the apparatus includes: a demodulationmodule, configured to receive one or more optical carriers in a sameoptical fiber, and demodulate transmission channels of a paralleltransmission frame from the optical carrier; an overhead parsing module,configured to parse an overhead of the transmission channels of theparallel transmission frame that are demodulated by the demodulationmodule, to obtain channels of the parallel transmission frame, where theoverhead includes a frame header identifier, a mapping overhead, and amanagement overhead that is extracted from one transmission channel inthe transmission channels of the parallel transmission frame, where themanagement overhead is used to centrally manage the channels of theparallel transmission frame, and bit rates of the transmission channelsof the parallel transmission frame are fixed; and a demapping module,configured to demap the client signal from the channels of the paralleltransmission frame after the mapping according to the frame headeridentifier, the mapping overhead, and the management overhead that areparsed by the overhead parsing module.

Beneficial effects of the technical solutions provided by theembodiments of the present invention are: a structure of a paralleltransmission frame is defined, a client signal, especially amultichannel parallel client signal, is mapped into transmissionchannels of the parallel transmission frame, and the transmissionchannels are modulated onto one or more optical carriers in a sameoptical fiber, which greatly simplifies processing complexity foradapting the multichannel parallel client signal, circumvents anexisting processing process of “multiplexing, distribution, andmultiplexing”, simplifies a signal adaptation process, and preventssetting a large number of buffers at a receiving end to compensate for adelay among multiple transmission channels, thereby saving costs.Therefore, a transport network can adapt to a change in a client signaland optical layer spectral bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly introduces theaccompanying drawings required for describing the embodiments.Apparently, the accompanying drawings in the following description showmerely some embodiments of the present invention, and a person ofordinary skill in the art may still derive other drawings from theseaccompanying drawings without creative efforts.

FIG. 1 is a schematic structural diagram of an OTN in the prior art;

FIG. 2 is a schematic diagram of transmission channels of a paralleltransmission frame according to an embodiment;

FIG. 3 is a schematic diagram of a frame structure of one oftransmission channels that is of a parallel transmission frame and has amanagement overhead according to an embodiment;

FIG. 4 is a flowchart of a method for transmitting a client signalaccording to an embodiment;

FIG. 5 is a flowchart of another method for transmitting a client signalaccording to an embodiment;

FIG. 6 is a flowchart of a method for receiving a client signalaccording to an embodiment;

FIG. 7 is a schematic diagram of an apparatus for transmitting a clientsignal according to an embodiment;

FIG. 8 is a schematic diagram of another apparatus for transmitting aclient signal according to an embodiment; and

FIG. 9 is a schematic diagram of an apparatus for receiving a clientsignal according to an embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

To make the objectives, technical solutions, and advantages of thepresent invention clearer, the following further describes theembodiments of the present invention in detail with reference to theaccompanying drawings.

An OTN frame structure is shown in FIG. 1. An OTN frame has a framestructure of 4×4080 bytes (that is, 4 rows×4080 columns). The OTN framestructure includes a framing area, an OTUk (Optical Channel TransportUnit, optical channel transport unit, where k=1, 2, 3, 4 whichcorrespond to rate levels of 2.5G, 10G, 40G, 100G respectively) OH(overhead area), an ODUk (optical channel data unit, where k=1, 2, 3, 4which correspond to the rate levels of 2.5G, 10G, 40G, 100Grespectively, or k=flex which indicates an any bit rate) OH, an OPUk(optical channel payload unit, where k=1, 2, 3, 4 which correspond tothe rate levels of 2.5G, 10G, 40G, 100G respectively, and k=flex whichindicates an any bit rate) OH, a payload area, an FEC area, and thelike. The framing area includes an FAS (frame alignment signal), wherethe OPUk OH is mainly used for client service mapping and adaptationmanagement, ODUk OH information is mainly used for managing andmonitoring the OTN frame, and OTUk OH information is mainly used formonitoring a transmission section. In addition, the FEC (forward errorcorrection) area is reserved.

To enable a transport network to adapt to a change in a client signaland optical layer spectral bandwidth, an embodiment provides a paralleltransmission frame. As shown in FIG. 2, the parallel transmission frameincludes n parallel transmission channels, where n is greater than orequal to 2, each transmission channel has a frame structure defined by aframe header, and bit rates of the transmission channels of the paralleltransmission frame are fixed. The parallel transmission frame includesan overhead area and a payload area. The payload area is used to carry aclient signal, and the overhead area is used to carry overheadinformation of the transmission channels. An overhead area of eachtransmission channel includes a frame header identifier, which is usedto define a start of the channel of the parallel transmission frame.Optionally, the overhead area of each transmission channel may furtherinclude a channel number identifier (ID), which is used to distinguisheach channel. It should be noted that, one of the transmission channelsof the parallel transmission frame further includes a managementoverhead, which is used to centrally manage the channels of the paralleltransmission frame. Which transmission channel the management overheadis specifically set on is not specifically limited in this embodiment.

In this embodiment, the management overhead includes: information aboutallocation of a corresponding channel of the parallel transmission frameto a corresponding client signal, which is similar to an OTN payloadstructure identifier (PSI: Payload Structure Identifier) and is used toindicate a client signal carrying status of the corresponding channel ofthe parallel transmission frame; and information indicating a type ofthe client signal carried by the corresponding channel of the paralleltransmission frame, which is similar to an OTN payload type (PT: PayloadType) identifier and is used to indicate the type of the client signalcarried by the corresponding channel of the parallel transmission frame.Optionally, the management overhead may further include: a lane monitor(LM, Lane monitor) overhead and/or automatic protection switching (APS:Automatic Protection Switching) overhead, where the lane monitoroverhead is used to monitor the channels of the parallel transmissionframe, and the automatic protection switching overhead is used toimplement automatic channel switching in case of a fault to recovertransmission of the client signal.

From a perspective of a management plane or a control plane, thesemanagement overheads can enable the physically independent channels ofthe parallel transmission frame to be treated as a unified whole formanagement; on a switching plane, multiple physically independentchannels of the parallel transmission frame may still be treated as aunified whole for cross-connection grooming. In a receiving direction ofan intermediate node, a central management overhead is set only on oneof the transmission channels, so that it is not required to parse allthe transmission channels of the parallel transmission frame on theintermediate node, and only the one transmission channel that carriesthe management overhead needs to be parsed, which greatly simplifiesoverhead processing complexity of the intermediate node.

In this embodiment, each transmission channel of the paralleltransmission frame may use a frame structure similar to that of an OTN,a frame structure similar to that of a GFP, or a frame structure similarto that of an Ethernet, which is not specifically limited in thisembodiment. In this embodiment, description is provided by using anexample in which each transmission channel of the parallel transmissionframe uses a frame structure similar to a TDM frame structure of an OTN.On a transmission channel of the parallel transmission frame, a part ofan overhead area is set as a management overhead based on an existingOTN frame structure, and no management overhead needs to be set on theother transmission channels of the parallel transmission frame. As shownin FIG. 3, FIG. 3 is a frame structure of a channel on which amanagement overhead is set, which includes a frame header identifier,the management overhead, a channel identifier (optional) and a payloadarea, and an optional FEC area that is reserved.

It should be noted that, a possible alternative solution for setting amanagement overhead on a transmission channel of a parallel transmissionframe is: the management overhead is set on one of the transmissionchannels of the parallel transmission frame, and management overheadswith a same value may also be set on the other transmission channels orsome of the other transmission channels of the parallel transmissionframe. However, any management overhead provides a function of centrallymanaging the transmission channels of the parallel transmission frame. Apurpose of setting multiple management overheads with the same value isto improve transmission reliability. For example, a multi-decisionmanner is used, and if multiple same management overheads are receivedin a receiving direction, it indicates that no error occurs when themanagement overheads are transmitted in a line.

It should be noted that, another possible alternative solution forsetting a management overhead on a transmission channel of a paralleltransmission frame is: an entire transmission channel of the paralleltransmission frame may be allocated to a management overhead to use; inthis case, the transmission channel of the parallel transmission framemay also be referred to as a management channel of the paralleltransmission frame. Optionally, an FEC area may also be allocated to allor some of the other transmission channels of the parallel transmissionframe on the management channel, and is used to implement a centralizedFEC function on the management channel.

In this embodiment, the bit rates of the transmission channels of theparallel transmission frame may be the same and may also be different.Preferably, for ease of implementation, it may be defined that rates (V)of all the transmission channels of the parallel transmission frame areequal. In addition, in order to adapt to a spectrum change at an opticallayer, that is, expanding from a conventional fixed 50 GHz spectral grid(ITU-T G.694) to a flexible spectral grid with a smaller granularity,where slot=12.5 GHz (a central frequency is 193.1 THz+n×slot/2, andspectral bandwidth is m×slot). Preferably, the rates of the transmissionchannels of the parallel transmission frame may be selected to be around12.5G, 25G, 50G, or 100G. Optionally, in order to be compatible with anexisting OTN system, a bit rate fitting an existing OTN line rate mayalso be selected, so that the existing OTN line rate can betransparently mapped into a payload area of a transmission channel ofthe parallel transmission frame. The present invention imposes only alimitation that the rates of the transmission channels of the paralleltransmission frame are fixed, but does not impose a limitation onspecific rates of the transmission channels of the parallel transmissionframe.

In this embodiment, a rate of the parallel transmission frame depends onthe number of transmission channels of the parallel transmission frameand the bit rates of the transmission channels, where the bit rates ofthe transmission channels of the parallel transmission frame are fixed.A flexible and changeable rate of the parallel transmission frame may beachieved by configuring a different number of channels. When the bitrates of the transmission channels of the parallel transmission frameare equal, after the number n of transmission channels of the paralleltransmission frame is determined, a total bit rate of the paralleltransmission frame is n*V. When the bit rates of the transmissionchannels of the parallel transmission frame are different, the total bitrate of the parallel transmission frame is a sum of the bit rates of thetransmission channels. Because of characteristics of being flexible andchangeable of the parallel transmission frame, if the rates of thetransmission channels of the parallel transmission frame are setappropriately, a super high OTN rate may be achieved easily. Forexample, for a 400G/1T OTU5, if a 10G level is selected for a rate of asingle transmission channel, a 400G-level OTU5 may be constructed whenn=40, and a 1T-level OTU5 may be constructed when n=100; if a 100G levelis selected for a rate of a single transmission channel, a 400G-levelOTU5 may be constructed by using only four transmission channels, and a1T-level OTU5 may be constructed by using only 10 transmission channels.

Based on the foregoing definition of the parallel transmission frame,the following methods for processing a client signal are provided in theembodiments:

Referring to FIG. 4, a method for transmitting a client signal isprovided in an embodiment, and includes the following steps.

101: Map the client signal into channels of a parallel transmissionframe, where the parallel transmission frame includes at least twochannels.

102: Add an overhead for the channels of the parallel transmission frameafter the mapping, to form transmission channels of the paralleltransmission frame, where a management overhead is added to one of thechannels of the parallel transmission frame after the mapping, themanagement overhead is used to centrally manage the channels of theparallel transmission frame after the mapping, and bit rates of thetransmission channels of the parallel transmission frame are fixed.

103: Modulate the transmission channels of the parallel transmissionframe onto one or more optical carriers in a same optical fiber, andtransmit the optical carrier after the modulation.

Beneficial effects of this embodiment are: a structure of a paralleltransmission frame is defined, a client signal, especially amultichannel parallel client signal, is mapped into transmissionschannels of the parallel transmission frame, which greatly simplifiesprocessing complexity for adapting the multichannel parallel clientsignal, circumvents an existing processing process of “multiplexing,distribution, and multiplexing”, and simplifies a signal adaptationprocess, thereby enabling a transport network to adapt to a change inthe client signal and optical layer spectral bandwidth.

Referring to FIG. 5, a method for transmitting a client signal isprovided in an embodiment, and includes the following steps.

201: Map the client signal into channels of a parallel transmissionframe.

In this embodiment, a transport network transmits the client signal to aclient. Based on the parallel transmission frame provided in thisembodiment, the client signal is mapped into the channels of theparallel transmission frame first. The number of channels of theparallel transmission frame may be 2, 5, 8, 15, and the like, which isnot specifically limited in this embodiment.

Further, in this embodiment, the client signal may be processeddifferently with respect to a feature of the client signal.Specifically, the mapping the client signal into channels of a paralleltransmission frame includes: when a rate of the client signal is greaterthan a rate of a single channel of the parallel transmission frame,splitting the client signal to obtain multiple client signals after thesplitting, and mapping the multiple client signals that are obtainedafter the splitting into corresponding channels of the paralleltransmission frame; or when a rate of the client signal is less than arate of a single channel of the parallel transmission frame, mapping theclient signal into one channel of the parallel transmission frame; orwhen the client signal is a multichannel parallel signal and a rate of asingle channel of the multichannel parallel client signal is less than arate of a single channel of the parallel transmission frame, mappingeach channel of the multichannel parallel client signal into acorresponding channel of the parallel transmission frame.

202: Add overheads for the channels of the parallel transmission frameafter the mapping, to form transmission channels of the paralleltransmission frame.

In this step, when the client signal is mapped into the channels of theparallel transmission frame, a corresponding overhead is added for eachchannel to an overhead area of the channel of the parallel transmissionframe. Specifically, each of the overheads added for the channels of theparallel transmission frame after the mapping includes: a frame headeridentifier and a mapping overhead, where the frame header identifier isused to identify a start of a channel of the parallel transmissionframe, and the mapping overhead is used to indicate a location, intowhich the client signal is mapped, in the channel.

Optionally, each of the overheads added for the channels of the paralleltransmission frame after the mapping further includes: one or more of achannel number identifier and a forward error correction FEC code, wherethe channel number identifier is used to distinguish each channel of theparallel transmission frame after the mapping, and the FEC code is usedto provide the channels of the parallel transmission frame with aforward error correction function.

In this embodiment, optionally, for the mapping overhead and the FEC,the mapping overhead and the FEC may be added to each transmissionchannel, and the mapping overhead and the FEC of each channel may alsobe centrally added to a channel. A manner of adding the mapping overheadand the FEC overhead that is used in a specific implementation processis not specifically limited in this embodiment.

In this embodiment, a management overhead is added to one of thechannels of the parallel transmission frame after the mapping, where themanagement overhead is used to centrally manage the channels of theparallel transmission frame after the mapping. In this embodiment,specifically, the management overhead includes: information aboutallocation of a corresponding channel of the parallel transmission frameto a corresponding client signal and/or information indicating a type ofa client signal carried by a corresponding channel of the paralleltransmission frame. Optionally, the management overhead furtherincludes: a lane monitor overhead and/or an automatic protectionswitching overhead, where the lane monitor overhead is used to monitorthe channels of the parallel transmission frame, and the automaticprotection switching overhead is used to implement automatic switchingof the channels of the parallel transmission frame in case of a fault,so as to recover transmission of the client signal.

It should be noted that, in this embodiment, the management overhead mayalso be added first, and then the mapping overhead is added to eachchannel. A specific adding sequence is not specifically limited in thisembodiment.

In addition, if packet encapsulation similar to a GFP (Generic FramingProcedure) manner is applied to the parallel transmission frame, a fixedfiller is included between frames, and is used to adapt a ratedifference between the client signal and the channel. If a TDM framemanner is used, no additional fixed filler needs to be added betweenframes. Rate adjustment may be performed between the client signal andthe channel in any one or more manners of a GMP (Generic MappingProcedure) or a conventional JC (justification control) byte, an NJO(negative justification opportunity) byte, and a PJO (positivejustification opportunity) byte, which is not specifically limited inthis embodiment.

203: Modulate the transmission channels of the parallel transmissionframe onto one or more optical carriers in a same optical fiber.

In this step, the transmission channels of the parallel transmissionframe are modulated onto the optical carrier in the same optical fiberfor transmission, where a single-carrier or multi-carrier transmissiontechnology may be used. For single-carrier transmission, code streams ofmultiple channels of the parallel transmission frame may be separatelymodulated to different phases of a single carrier, for example, a QPSKmodulation format is used. For multi-carrier transmission, one or morechannels of the parallel transmission frame may be modulated onto onesubcarrier according to a used modulation format, and then amulti-carrier signal is generated. Further optionally, an OFDMmulti-carrier transmission technology may be used, and differentsubcarriers may use different modulation formats, such as PSK, QPSK,4QAM, and 16QAM. Alternatively, each channel of the paralleltransmission frame may further be divided into multiple data streamswith a lower rate, and then the multiple data streams are modulated ontomultiple subcarriers.

In this embodiment, specifically, the modulating the transmissionchannels of the parallel transmission frame onto one or more opticalcarriers in a same optical fiber includes: separately modulating eachchannel in the transmission channels of the parallel transmission frameonto an optical subcarrier in a corresponding number of multiple opticalsubcarriers in the same optical fiber; or dividing the transmissionchannels of the parallel transmission frame into N groups oftransmission channels, where each group includes M transmissionchannels, and M is the number of subcarrier modulation phases,modulating each group of M transmission channels onto one opticalsubcarrier, and separately modulating the N groups of transmissionchannels onto N optical subcarriers in the same optical fiber; ormultiplexing the transmission channels of the parallel transmissionframe into one data stream or data streams whose number is less than thenumber of transmission channels, and modulating the one data stream orthe data streams whose number is less than the number of transmissionchannels onto a single optical carrier or a corresponding number ofoptical carriers in the same optical fiber; or splitting eachtransmission channel of the parallel transmission frame into multipledata streams with a preset rate, and then separately modulating themultiple data streams corresponding to each transmission channel ontomultiple subcarriers in the same optical fiber, where the preset raterefers to a rate that is lower than a rate of a single transmissionchannel of the parallel transmission frame, which is not specificallylimited in this embodiment.

In this embodiment, the transmission channels of the paralleltransmission frame are modulated onto the optical carrier in the sameoptical fiber. In the case of a single carrier, all the transmissionchannels of the parallel transmission frame are transmitted only in asingle optical carrier, and the single carrier will be finally modulatedto the same optical fiber for transmission; therefore, differentindependent transmission channels of the parallel transmission frame areeventually transmitted on a same optical path, a delay, on the opticalpath, of different transmission channels of the parallel transmissionframe may be ignored, and a delay, in electrical processing, ofdifferent transmission channels of the parallel transmission frame maybe controlled by using an internal circuit. In the case of multiplecarriers, because this embodiment imposes a limitation that all multiplecarriers corresponding to all different transmission channels of thesame parallel transmission frame are eventually modulated to a sameoptical fiber for transmission, different independent transmissionchannels of the parallel transmission frame are also eventuallytransmitted on a same optical path in the case of the multiple carriers.

Therefore, in the case of the multiple carriers, a delay, on the opticalpath, of different transmission channels of the parallel transmissionframe may also be ignored. In the case of the multiple carriers, adelay, in electrical processing, of different transmission channels ofthe parallel transmission frame is also consistent with that in the caseof a single carrier, and may be controlled by using an internal circuit.Therefore, in this embodiment, among overheads of different transmissionchannels of the parallel transmission frame, a delay compensationoverhead that is particularly used for controlling or compensatingdifferent independent transmission channels of the parallel transmissionframe is excluded, and an MFI1/MFI2 (multiframe indicator) functionoverhead similar to that in an OTN or SDH (Synchronous DigitalHierarchy, synchronous digital hierarchy) virtual concatenationtechnology is excluded.

In this embodiment, different transmission channels of the paralleltransmission frame are modulated onto the optical carrier in the sameoptical fiber, and setting the delay compensation overhead with complexprocessing is prevented on the different transmission channels, so thatit is prevented that a large number of buffers are set on a receivingend to compensate for a delay among multiple different transmissionchannels, which saves plenty of costs.

204: Transmit the optical carrier after the modulation.

In this step, after the signal transmission channels of the paralleltransmission frame are modulated onto the optical carrier in the sameoptical fiber, the client signal is transmitted to the receiving end byusing the optical carrier. It should be noted that, in this embodiment,when the optical carriers, corresponding to different transmissionchannels of the parallel transmission frame, in the same optical fiberare processed on an optical carrier switching node, for example, an OADM(optical add-drop multiplexer) node or a ROADM (reconfigurable opticaladd-drop multiplexer) node, the optical carriers, corresponding to thedifferent transmission channels of the parallel transmission frame, inthe same optical fiber must be switched as a group in a unified manner,so as to prevent that the optical carriers in the same optical fiber areswitched into different optical fibers, and prevent bringing a largeoptical path delay between the different transmission channels.

In order to make a person skilled in the prior art better understand themethod for transmitting a client signal provided in the presentinvention, the following example is used:

A frame structure of a parallel transmission frame uses an existing OTNframe structure; after a single-channel rate of the paralleltransmission frame is determined, for example, a single-channel rate ofa 12.5G level is selected, the number of channels of the paralleltransmission frame may be configured flexibly, thereby obtaining aseries of flexible transmission line bandwidth OTUflex(n)=12.5G*n. Forexample, at a site A, when a 40GE four-channel parallel signal(40GBASE-R) needs to be aggregated with a 10GE signal (10GBASE-R), it isconfigured that n=5, and then total bandwidth of the paralleltransmission frame is about 12.5*5=62.5G. Each signal of the 40GEfour-channel parallel signal may be separately mapped into four channelsof an OTUflex(n=5) by using the GMP, and the 10GE signal may be mappedinto one channel of the OTUflex(n=5) by using the GMP. This solutionachieves efficient transmission of 40GE and 10GE signals by configuringa flexible OTUflex, which greatly saves bandwidth and simplifies logicprocessing.

Beneficial effects of this embodiment are: a structure of a paralleltransmission frame is defined, a client signal, especially amultichannel parallel client signal, is mapped into transmissionchannels of the parallel transmission frame, and the transmissionchannels are modulated onto one or more optical carriers in a sameoptical fiber, which greatly simplifies processing complexity foradapting the multichannel parallel client signal, circumvents anexisting processing process of “multiplexing, distribution, andmultiplexing”, simplifies a signal adaptation process, and preventssetting a large number of buffers at a receiving end to compensate for adelay among multiple transmission channels, thereby saving costs.Therefore, a transport network can adapt to a change in a client signaland optical layer spectral bandwidth. A rate of the paralleltransmission frame may change flexibly; therefore, a flexibletransmission line interface can be conveniently implemented, so as toresolve a problem of a mismatch between service bandwidth and linebandwidth, thereby improving bandwidth usage. In addition, each channeluses a low-rate interface, which facilitates chip implementation andhelps the transport network to evolve towards a super high speed.

Referring to FIG. 6, a method for receiving a client signal is providedin an embodiment, and includes the following steps.

301: Receive one or more optical carriers in a same optical fiber, anddemodulate transmission channels of a parallel transmission frame fromthe optical carrier.

A method for performing demodulation on the optical carrier in the sameoptical fiber is similar to that in the prior art, and is not describedin this embodiment again.

302: Parse an overhead of the transmission channels of the paralleltransmission frame, to obtain channels of the parallel transmissionframe, where the overhead includes a frame header identifier, a mappingoverhead, and a management overhead that is extracted from onetransmission channel in the transmission channels of the paralleltransmission frame, where the management overhead is used to centrallymanage the transmission channels of the parallel transmission frame, andbit rates of the transmission channels of the parallel transmissionframe are fixed.

In this embodiment, the management overhead includes: information aboutallocation of a corresponding channel of the parallel transmission frameto a corresponding client signal and/or information indicating a type ofa client signal carried by a corresponding channel of the paralleltransmission frame.

The parsing overhead information of the transmission channels of theparallel transmission frame, to obtain channels of the paralleltransmission frame includes: obtaining the frame header identifier ofeach transmission channel of the parallel transmission frame; andidentifying a frame structure of each transmission channel according tothe frame header identifier of each transmission channel of the paralleltransmission frame, to obtain the channels of the parallel transmissionframe.

Further, the parsing overhead information of the transmission channelsof the parallel transmission frame, to obtain channels of the paralleltransmission frame further includes performing forward error correctionFEC code processing on each transmission channel.

303: Demap the client signal from the transmission channels of theparallel transmission frame according to the frame header identifier,the mapping overhead, and the management overhead.

The demapping, according to the mapping overhead, and the informationabout the allocation of the corresponding channel of the paralleltransmission frame to the corresponding client signal and/or theinformation indicating the type of the client signal carried by thecorresponding channel of the parallel transmission frame in themanagement overhead is similar to that in the prior art, and is notdescribed in this embodiment again.

Beneficial effects of this embodiment are: one or more optical carriersin a same optical fiber are received, and transmission channels of aparallel transmission frame are demodulated from the optical carrier; anoverhead of the transmission channels of the parallel transmission frameis parsed, to obtain channels of the parallel transmission frame; theclient signal is demapped from the channels of the parallel transmissionframe according to a mapping overhead and a management overhead. In thisway, low-speed processing of multichannelization is implemented whenoptically transmitted data with higher spectral efficiency is decoded,thereby reducing complexity and costs of processing by a receiving end.

Referring to FIG. 7, an apparatus for transmitting a client signal isprovided in an embodiment, and includes: a mapping module 401, anoverhead adding module 402, and a modulation and transmission module403.

The mapping module 401 is configured to map the client signal intochannels of a parallel transmission frame, where the paralleltransmission frame includes at least two channels.

The overhead adding module 402 is configured to add an overhead for thechannels of the parallel transmission frame after the mapping module 401performs the mapping, to form signal transmission channels of theparallel transmission frame, where a management overhead is added to oneof the channels of the parallel transmission frame after the mapping,the management overhead is used to centrally manage the channels of theparallel transmission frame after the mapping, and bit rates of thetransmission channels of the parallel transmission frame are fixed.

The modulation and transmission module 403 is configured to modulate thetransmission channels of the parallel transmission frame that are formedby the overhead adding module 402 onto one or more optical carriers in asame optical fiber, and transmit the optical carrier after themodulation.

A rate of the parallel transmission frame depends on the number oftransmission channels of the parallel transmission frame and the bitrates of the transmission channels.

Optionally, the apparatus further includes a channel adjustment module,configured to: when the bit rates of the transmission channels of theparallel transmission frame are equal, adjust the number of transmissionchannels of the parallel transmission frame to form a paralleltransmission frame with a changeable rate.

Referring to FIG. 8, optionally, the mapping module 401 includes a firstmapping unit 401 a, configured to: when a rate of the client signal isgreater than a transmission rate of a single channel of the paralleltransmission frame, split the client signal to obtain multiple clientsignals after the splitting, and map the multiple client signals thatare obtained after the splitting into corresponding channels of theparallel transmission frame; or a second mapping unit 401 b, configuredto: when a rate of the client signal is less than a transmission rate ofa single channel of the parallel transmission frame, map the clientsignal into one channel of the parallel transmission frame; or a thirdmapping unit 401 c, configured to: when the client signal is amultichannel parallel signal and a rate of a single channel of themultichannel parallel client signal is less than a rate of a singlechannel of the parallel transmission frame, map each channel of themultichannel parallel client signal into a corresponding channel of theparallel transmission frame.

In this embodiment, the overhead added for the channels of the paralleltransmission frame after the mapping includes a frame header identifierand a mapping overhead, where the frame header identifier is used toidentify a start of a channel of the parallel transmission frame, andthe mapping overhead is used to indicate a location, into which theclient signal is mapped, in the channel.

Optionally, the overhead added for the channels of the paralleltransmission frame after the mapping further includes one or more of achannel number identifier and a forward error correction FEC code, wherethe channel number identifier is used to distinguish each channel of theparallel transmission frame after the mapping, and the FEC code is usedto provide the channels of the parallel transmission frame with aforward error correction function.

In this embodiment, the management overhead includes information aboutallocation of a corresponding channel of the parallel transmission frameto a corresponding client signal and/or information indicating a type ofa client signal carried by a corresponding channel of the paralleltransmission frame.

Optionally, the management overhead further includes a lane monitoroverhead and/or an automatic protection switching overhead, where thelane monitor overhead is used to monitor the channels of the paralleltransmission frame, and the automatic protection switching overhead isused to implement automatic switching of the channels of the paralleltransmission frame in case of a fault, so as to recover transmission ofthe client signal.

Optionally, referring to FIG. 8, the modulation and transmission module403 includes a first modulation unit 403 a, configured to separatelymodulate each channel in the transmission channels of the paralleltransmission frame onto an optical subcarrier in a corresponding numberof multiple optical subcarriers in the same optical fiber; or a secondmodulation unit 403 b, configured to divide the transmission channels ofthe parallel transmission frame into N groups of transmission channels,where each group includes M transmission channels, and M is the numberof subcarrier modulation phases, modulate each group of M transmissionchannels onto one optical subcarrier, and separately modulate the Ngroups of transmission channels onto N optical subcarriers in the sameoptical fiber; or a third modulation unit 403 c, configured to multiplexthe transmission channels of the parallel transmission frame into onedata stream or data streams whose number is less than the number oftransmission channels, and modulate the one data stream or the datastreams whose number is less than the number of transmission channelsonto a single optical carrier or a corresponding number of opticalcarriers in the same optical fiber; or a fourth modulation unit 403 d,configured to split each transmission channel of the paralleltransmission frame into multiple data streams with a preset rate, andseparately modulate the multiple data streams corresponding to eachsplit transmission channel onto multiple subcarriers in the same opticalfiber.

Beneficial effects of this embodiment are: a structure of a paralleltransmission frame is defined, a client signal, especially amultichannel parallel client signal, is mapped into transmissionchannels of the parallel transmission frame, and the transmissionchannels are modulated onto one or more optical carriers in a sameoptical fiber, which greatly simplifies processing complexity foradapting the multichannel parallel client signal, circumvents anexisting processing process of “multiplexing, distribution, andmultiplexing,” simplifies a signal adaptation process, and preventssetting a large number of buffers at a receiving end to compensate for adelay among multiple transmission channels, thereby saving costs.Therefore, a transport network can adapt to a change in a client signaland optical layer spectral bandwidth.

Referring to FIG. 9, an apparatus for receiving a client signal isprovided in an embodiment, and includes: a demodulation module 501, anoverhead parsing module 502, and a demapping module 503.

The demodulation module 501 is configured to receive one or more opticalcarriers in a same optical fiber, and demodulate transmission channelsof a parallel transmission frame from the optical carrier.

The overhead parsing module 502 is configured to parse an overhead ofthe transmission channels of the parallel transmission frame that aredemodulated by the demodulation module 501, to obtain channels of theparallel transmission frame, where the overhead includes a frame headeridentifier, a mapping overhead, and a management overhead that isextracted from one transmission channel in the transmission channels ofthe parallel transmission frame, where the management overhead is usedto centrally manage the channels of the parallel transmission frame, andbit rates of the transmission channels of the parallel transmissionframe are fixed.

The demapping module 503 is configured to demap the client signal fromthe transmission channels of the parallel transmission frame accordingto the frame header identifier, the mapping overhead, and the managementoverhead that are parsed by the overhead parsing module 502.

Beneficial effects of this embodiment are: one or more optical carriersin a same optical fiber are received, and transmission channels of aparallel transmission frame are demodulated from the optical carrier; anoverhead of the transmission channels of the parallel transmission frameis parsed, to obtain channels of the parallel transmission frame; theclient signal is demapped from the channels of the parallel transmissionframe according to a frame header identifier, a mapping overhead, and amanagement overhead. In this way, low-speed processing ofmultichannelization is implemented when optically transmitted data withhigher spectral efficiency is decoded, thereby reducing complexity andcosts of processing by a receiving end, and preventing setting a largenumber of buffers on the receiving end to compensate a delay amongmultiple transmission channels, which saves plenty of costs.

The apparatus provided in this embodiment may specifically belong to asame idea as the method embodiment; for a specific implementationprocess thereof, reference may be made to the method embodiment, whichis not described herein again.

It should be noted that, in the foregoing apparatus embodiments fortransmitting and receiving a client signal, various modules included aredivided merely according to a logical function, and the division is notlimited to the foregoing division as long as a corresponding functioncan be implemented. In addition, specific names of the variousfunctional modules are merely for ease of distinguishment from eachother, but are not intended to limit the protection scope of the presentinvention.

A person of ordinary skill in the art may understand that all or a partof the steps of the embodiments may be implemented by hardware or aprogram instructing relevant hardware. The program may be stored in acomputer readable storage medium. The storage medium may include: aread-only memory, a magnetic disk, or an optical disc.

The foregoing descriptions are merely exemplary embodiments of thepresent invention, but are not intended to limit the present invention.Any modification, equivalent replacement, and improvement made withoutdeparting from the spirit and principle of the present invention shallfall within the protection scope of the present invention.

What is claimed is:
 1. A method for transmitting a client signal, themethod comprising: mapping the client signal into channels of a paralleltransmission frame, wherein the parallel transmission frame comprises atleast two channels; adding an overhead for the channels of the paralleltransmission frame after the mapping, to form transmission channels ofthe parallel transmission frame, wherein a management overhead is addedto one of the channels of the parallel transmission frame after themapping, the management overhead being used to centrally manage thechannels of the parallel transmission frame after the mapping, andwherein bit rates of the transmission channels of the paralleltransmission frame are fixed; modulating the transmission channels ofthe parallel transmission frame onto one or more optical carriers in asame optical fiber; and transmitting the optical carrier after themodulation.
 2. The method according to claim 1, wherein a rate of theparallel transmission frame depends on the number of transmissionchannels of the parallel transmission frame and the bit rates of thetransmission channels.
 3. The method according to claim 2, wherein thebit rates of the transmission channels of the parallel transmissionframe are equal and the number of transmission channels of the paralleltransmission frame is adjusted to form a parallel transmission framewith a changeable rate.
 4. The method according to claim 1, whereinmapping the client signal into channels of a parallel transmission framecomprises: when a rate of the client signal is greater than a rate of asingle channel of the parallel transmission frame, splitting the clientsignal to obtain multiple client signals after the splitting, andmapping the multiple client signals that are obtained after thesplitting into corresponding channels of the parallel transmissionframe; when a rate of the client signal is less than a rate of a singlechannel of the parallel transmission frame, mapping the client signalinto one channel of the parallel transmission frame; and when the clientsignal is a multichannel parallel client signal and a rate of a singlechannel of the multichannel parallel client signal is less than a rateof a single channel of the parallel transmission frame, mapping eachchannel of the multichannel parallel client signal into a correspondingchannel of the parallel transmission frame.
 5. The method according toclaim 1, wherein the overhead added for the channels of the paralleltransmission frame after the mapping comprises a frame header identifierand a mapping overhead, wherein the frame header identifier is used toidentify a start of a channel of the parallel transmission frame and themapping overhead is used to indicate a location, into which the clientsignal is mapped, in the channel.
 6. The method according to claim 5,wherein the overhead added for the channels of the parallel transmissionframe after the mapping further comprises one or more of a channelnumber identifier and a forward error correction (FEC) code, wherein thechannel number identifier is used to distinguish each channel of theparallel transmission frame after the mapping, and the FEC code is usedto provide the channels of the parallel transmission frame with aforward error correction function.
 7. The method according to claim 1,wherein the management overhead comprises information about allocationof a corresponding channel of the parallel transmission frame to acorresponding client signal and/or information indicating a type of aclient signal carried by a corresponding channel of the paralleltransmission frame.
 8. The method according to claim 7, wherein themanagement overhead further comprises a lane monitor overhead and/or anautomatic protection switching overhead, wherein the lane monitoroverhead is used to monitor the channels of the parallel transmissionframe, and the automatic protection switching overhead is used toimplement automatic switching of the channels of the paralleltransmission frame in case of a fault, so as to recover transmission ofthe client signal.
 9. The method according to claim 1, wherein themodulating the transmission channels of the parallel transmission frameonto one or more optical carriers in a same optical fiber comprises:separately modulating each channel in the transmission channels of theparallel transmission frame onto an optical subcarrier in acorresponding number of multiple optical subcarriers in the same opticalfiber; or dividing the transmission channels of the paralleltransmission frame into N groups of transmission channels, wherein eachgroup comprises M transmission channels, and M is the number ofsubcarrier modulation phases, modulating each group of M transmissionchannels onto one optical subcarrier, and separately modulating the Ngroups of transmission channels onto N optical subcarriers in the sameoptical fiber; or multiplexing the transmission channels of the paralleltransmission frame into one data stream or data streams whose number isless than the number of transmission channels, and modulating the onedata stream or the data streams whose number is less than the number oftransmission channels onto a single optical carrier or a correspondingnumber of optical carriers in the same optical fiber; or splitting eachtransmission channel of the parallel transmission frame into multipledata streams with a preset rate, and separately modulating the multipledata streams corresponding to each split transmission channel ontomultiple subcarriers in the same optical fiber.
 10. A method forreceiving a client signal, the method comprising: receiving one or moreoptical carriers in a same optical fiber; demodulating transmissionchannels of a parallel transmission frame from the optical carrier;parsing an overhead of the transmission channels of the paralleltransmission frame, to obtain channels of the parallel transmissionframe, wherein the overhead comprises a frame header identifier, amapping overhead, and a management overhead that is extracted from onetransmission channel in the transmission channels of the paralleltransmission frame, wherein the management overhead is used to centrallymanage the channels of the parallel transmission frame, and bit rates ofthe transmission channels of the parallel transmission frame are fixed;and demapping the client signal from the channels of the paralleltransmission frame according to the frame header identifier, the mappingoverhead, and the management overhead.
 11. An apparatus comprising: aprocessor; and a computer-readable storage medium storing a program tobe executed by the processor, the program including instructions for:mapping the client signal into channels of a parallel transmissionframe, wherein the parallel transmission frame comprises at least twotransmission channels; adding an overhead for the channels of theparallel transmission frame after the mapping module performs themapping, to form transmission channels of the parallel transmissionframe, wherein a management overhead is added to one of the channels ofthe parallel transmission frame after the mapping, the managementoverhead is used to centrally manage the channels of the paralleltransmission frame after the mapping, and bit rates of the transmissionchannels of the parallel transmission frame are fixed; modulating thetransmission channels of the parallel transmission frame that are formedby the overhead adding module onto one or more optical carriers in asame optical fiber; and transmitting the optical carrier after themodulation.
 12. The apparatus according to claim 11, wherein a rate ofthe parallel transmission frame depends on the number of transmissionchannels of the parallel transmission frame and the bit rates of thetransmission channels.
 13. The apparatus according to claim 11, whereinthe program includes further instructions for adjusting the number oftransmission channels of the parallel transmission frame to form aparallel transmission frame with a changeable rate when the bit rates ofthe transmission channels of the parallel transmission frame are equal.14. The apparatus according to claim 11, wherein the program includesfurther instructions for: when a rate of the client signal is greaterthan a rate of a single channel of the parallel transmission frame,splitting the client signal to obtain multiple client signals after thesplitting, and mapping the multiple client signals that are obtainedafter the splitting into corresponding channels of the paralleltransmission frame; when a rate of the client signal is less than a rateof a single channel of the parallel transmission frame, mapping theclient signal into one channel of the parallel transmission frame; andwhen the client signal is a multichannel parallel client signal and arate of a single channel of the multichannel parallel client signal isless than a rate of a single channel of the parallel transmission frame,mapping each channel of the multichannel parallel client signal into acorresponding channel of the parallel transmission frame.
 15. Theapparatus according to claim 11, wherein the overhead added for thechannels of the parallel transmission frame after the mapping comprisesa frame header identifier and a mapping overhead, wherein the frameheader identifier is used to identify a start of a channel of theparallel transmission frame, and the mapping overhead is used toindicate a location, into which the client signal is mapped, in thechannel.
 16. The apparatus according to claim 15, wherein the overheadadded for the channels of the parallel transmission frame after themapping further comprises one or more of a channel number identifier anda forward error correction FEC code, wherein the channel numberidentifier is used to distinguish each channel of the paralleltransmission frame after the mapping, and the FEC code is used toprovide the channels of the parallel transmission frame with a forwarderror correction function.
 17. The apparatus according to claim 11,wherein the management overhead comprises information about allocationof a corresponding channel of the parallel transmission frame to acorresponding client signal and/or information indicating a type of aclient signal carried by a corresponding channel of the paralleltransmission frame.
 18. The apparatus according to claim 17, wherein themanagement overhead further comprises a lane monitor overhead and/or anautomatic protection switching overhead, wherein the lane monitoroverhead is used to monitor the channels of the parallel transmissionframe, and the automatic protection switching overhead is used toimplement automatic switching of the channels of the paralleltransmission frame in case of a fault, so as to recover transmission ofthe client signal.
 19. The apparatus according to claim 11, wherein theprogram includes further instructions for: separately modulating eachchannel in the transmission channels of the parallel transmission frameonto an optical subcarrier in a corresponding number of multiple opticalsubcarriers in the same optical fiber; or dividing the transmissionchannels of the parallel transmission frame into N groups oftransmission channels, wherein each group comprises M transmissionchannels, and M is the number of subcarrier modulation phases,modulating each group of M transmission channels onto one opticalsubcarrier, and separately modulating the N groups of transmissionchannels onto N optical subcarriers in the same optical fiber; ormultiplexing the transmission channels of the parallel transmissionframe into one data stream or data streams whose number is less than thenumber of transmission channels, and modulating the one data stream orthe data streams whose number is less than the number of transmissionchannels onto a single optical carrier or a corresponding number ofoptical carriers in the same optical fiber; or splitting eachtransmission channel of the parallel transmission frame into multipledata streams with a preset rate, and separately modulating the multipledata streams corresponding to each split transmission channel ontomultiple subcarriers in the same optical fiber.
 20. An apparatuscomprising: a processor; and a computer-readable storage medium storinga program to be executed by the processor, the program includinginstructions for: receiving one or more optical carriers in a sameoptical fiber; demodulating transmission channels of a paralleltransmission frame from the optical carrier; parsing an overhead of thetransmission channels of the parallel transmission frame that aredemodulated by the demodulation module, to obtain channels of theparallel transmission frame, wherein the overhead comprises a frameheader identifier, a mapping overhead, and a management overhead that isextracted from one transmission channel in the transmission channels ofthe parallel transmission frame, wherein the management overhead is usedto centrally manage the channels of the parallel transmission frame, andbit rates of the transmission channels of the parallel transmissionframe are fixed; and demapping the client signal from the channels ofthe parallel transmission frame after the mapping according to the frameheader identifier, the mapping overhead, and the management overheadthat are parsed by the overhead parsing module.